China has become notorious for the extent and sophistication of its Internet censorship. The government constantly adjusts its roster of banned Web sites. Search engines filter content, leaving only pro-government information on sensitive topics. Companies that provide space to bloggers censor hundreds of key words, such as "democracy," "Falun Gong," and "freedom." Chat rooms are monitored by tens of thousands of government workers, who remove offending posts. E-mail is subject to censorship, although less likely to be blocked than public communications. Even text messages are now perused by the authorities.

But China is hardly alone in its vigilance. The map at right, based on research by Reporters Without Borders, a free-press watchdog group, shows the state of Internet freedom in fifty-five countries worldwide, based on how much of the Web is blocked and how vulnerable citizens are to government intimidation for unsanctioned use.

For the most part, the countries that police the Web most thoroughly are the ones you'd expect: Iran, China, and Vietnam are among the most aggressive, blocking a wide range of political, religious, human-rights, and vice-related sites while tracking Internet users carefully. In Burma and Cuba, only a tiny fraction of users can connect to the Internet at all; the rest can access only their country's intranet, composed mostly of business and government propaganda sites. Several states filter only minimally but make examples of those who speak up on the Web: there are currently fifty-five dissidents imprisoned for online activities worldwide—forty-eight in China, two in Vietnam, two in Iran, and one each in the Maldives, Tunisia, and Syria.

But liberal democracies also filter the Web. Google first censored its search engine on a state's behalf not in January to assist China but nearly four years ago to comply with hate-speech codes in Germany, France, and Switzerland. In America, Pennsylvania's then-attorney general enforced a law requiring Internet service providers to block sites hosting child porn, though the courts have since deemed that law unconstitutional.

Worldwide, the number one target of government filters is not political speech but pornography. In Islamic states, sites featuring lingerie, alcohol, drugs, gay or lesbian images, evangelism, sex education, and criticism of Islam are often blocked. This emphasis on moral matters may reflect the hierarchy of concerns of many governments, but sites catering to vice are also the easiest to block: many government censors rely on off-the-shelf filtering software—originally built to keep employees from engaging in dubious workplace activities—which features ready-made blacklists of offensive sites by category. (This sort of filtering can be clumsy, and inevitably leads to inadvertent blocking. For instance, smut filters have blocked the tourism site of the English county of Essex and temporarily stopped the residents of Scunthorpe from logging on to AOL.)

While China has proved that the mass of casual surfers can be effectively blinkered by a committed regime, experienced users can find ways through the firewall. Only the most dedicated governments can keep blacklists up to date on the ever-changing Web, and very often simply trying an alternate address or dropping the prefix "www" will allow access to a banned site. Bloggers can also slip obvious misspellings of banned words past the censors. In Cuba, a black market in Internet access has sprung up.

New software and Web services increasingly allow Internet users to bypass filters. Dissident exiles and groups like the OpenNet Initiative and Electronic Frontier Foundation actively update and distribute such software in a race to stay ahead of the censors, although the censors are fighting back by blocking access to those resources, and even allegedly attacking those
writing the codes (a Falun Gong specialist in circumventing Chinese filters was rolled in a carpet and beaten, and the computers taken from his Atlanta home, in February).

Like so much early hype surrounding the Internet, talk of the Web's potential as a democratizing force has far exceeded the reality. To date, relatively well-wired countries such as the United Arab Emirates, Singapore, and China have reaped many of the economic benefits of the Web while still stifling the flow of free information. Censorship techniques in these places have become more precise and supple over time.

But it's still too soon to know whether censors will be able to keep the Web under heel. Most governments are not sophisticated in their attempts at censorship—they rely on simple filtering technologies that can be defeated by a determined political opposition. Even in China, information is seeping through. The regime is having trouble staying on top of the 111 million residents now online—less than 10 percent of the country's population. It's hard to imagine how it will keep up as that number swells.